(1) Field of the Invention
The present invention relates to exercise of control over the flow of fluids and particularly to achieving unidirectional flow of gas into a compressor and discharge of gas from a compressor. More specifically, this invention is directed to flow control devices and particularly to one-way flow valves. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The present invention relates to one-way flow or check valves of the type known in the art as "reed" or "feather" valves. Valves of this type have long been known and are exemplified by U.S. Pat. Nos. 1,534,260, 1,754,747 and 2,092,088. These valves, which will hereinafter be referred to as "feather" valves, are used in both the inlet and discharge lines of reciprocating type compressors. Such feather valves are critical to proper operation of reciprocating type compressors and a typical compressor may employ from two to sixteen valves per cylinder. Accordingly, in a large compressor installation, there may be in excess of one hundred feather valves and the failure of any one valve (i.e one feather in one valve) will result in shutdown of the compressor.
To briefly describe a typical prior art feather valve, the device includes a valve seat defining member consisting of a flat plate which has a plurality of parallelly oriented slots or ports extending therethrough. A member known as a guard faces the valve seat and is also provided with parallel through slots or ports; the slots in the guard being offset in staggered relation with respect to the slots in the seat. The guard also includes, between the through slots, curved recesses. Flexible strips or feathers are sandwiched between the seat and guard and are constrained so as to be in alignment with the slots in the seat. The strips, when in the seated position, completely cover the slots that form the air passages through the seat whereby the valve will be in the closed condition. The strips are restrained to prevent uncovering of these slots or ports except by flexure into the curved recesses, also known as profiles, in the guard. Considering operation of a feather valve on the suction side of a compressor, the valve is in the air intake with the valve seat on the upstream side and the valve guard downstream. On the suction stroke negative pressure in the cylinder results in air being drawn into the cylinder through the valves with the strips flexing into the profiles in the guard and thus permitting flow of air through the offset slots in the seat and guard. On the compression stroke the strips or feathers of the inlet valve are forced flat against the surface of the seat thereby sealing the slots and permitting the air which has been drawn in to be compressed. On the discharge side of the compressor the valves are positioned so that the discharge pressure flexes the strips to permit flow through the valves.
The operating environment of a feather valve of the type briefly discussed above may, as noted, be in the inlet or discharge line of a reciprocating compressor. In the case of high speed compressor; i.e., those which operate at speeds in excess of 800 rpm; a typical prior art feather valve has had a service life of less than one hundred hours. This comparatively short service life results from fatigue of the flexing strips which function as the moving valve members. In use the strips are subjected to stresses caused by bending and impact. The impact of the strip on the guard when the valve opens, and the vibration induced in the moving element following the impact, are important causes of fatigue and subsequent valve failure. Other causes of valve failure are thought to be corrosion fatigue and thermal-shock.
Attempts to overcome the above briefly discussed problems, and thereby provide feather valves having an increased service life, have concentrated upon the judicious selection of materials, enhancement of the structural integrity of the strips through resort to use of double flexing strips or strips of increased thickness and to coating relatively moving contacting surfaces with materials having a low coefficient of friction so as to minimize any increase in temperature of the parts resulting from friction. These prior art techniques have not resulted in significant improvements in valve life expectancy.